Abstract

An operator required straddle related interventions to be carried out on one of their platforms in the North
Sea, for both straddle retrieval and straddle deployment purposes. For these they were seeking innovative
solutions to deliver more efficient and effective operations providing time and cost savings. The first
operation described in the paper was a straddle packer deployment, which, done conventionally using coiled
tubing, would have required nine runs to install the 100-meter assembly. This was due to the limited rig up
height available. The second operation was to pull a shallow set straddle before setting a plug and punching
the tubing as part of a plug and abandon operation. Here, scale had accumulated above the straddle which
first needed to be removed to enable the removal of the straddle itself.

For both operations, a solution was devised that overcame the challenges and inefficiencies of the more
traditional methods, be that using coiled tubing or slickline. In the first (straddle packer deployment), an
electric line tractor was used to aid in-well straddle assembly. The tractor's real-time tension/compression
readings would provide accurate and controlled deployment and a precise measurement of the over-pull
verification once set. The solution provided more rig up height, enabling surface assembly of spacer pipe
sections, hence fewer runs for the full straddle system deployment. For the second (straddle packer retrieval),
historically such scale removal would be performed by slickline broaching—a time consuming multi-run
method. Instead, an electric line powered debris removal tool string was used, removing the scale in hours
instead of days. Critical toolstring space-out through the blowout preventer (BOP) stack was managed.
Furthermore, an electric line powered stroker was used to retrieve the straddle sections.

The application of electric line based intervention technologies provided direct and indirect efficiencies.
In the first operation, the electric line deployment of the straddle packer assembly was completed in only six
runs compared to the nine runs required if coiled tubing was used, which delivered a time saving of almost
two days. Pre-job simulations were carried out to optimise the deployment tool string design. During the
second operation, the cleanout mill string, with collection chambers added purely to manage the string space
out through the BOP stack, also provided better centralisation for the milling operation. With this operation
occurring within the marine riser section, hydraulic oil specification was optimised for 1 °C operation.

Advantages brought about through the use of electric line deployed powered mechanical tools were
apparent in both operations. The depth resolution, coupled with the real-time surface read-out toolstring
command—provided by electric line—enabled fast, precise and controlled operations, including delicate
straddle tagging without risk of damage. Both operations were executed successfully.